RAPPORTS. XIII C2: THOMPSON — 20 — 



of the Cod on the various stations, that is to say the ages which correspond approxi- 

 mately to that inter-quartile zone which has been discussed in the preceding paragraph. 

 It will be seen that within the Firth itself it is the groups I, II, and III, that predominate 

 in varying proportions; only at Station IX, outside the Firth itself, do older Cod become 

 predominant, in the sense in which we are now using the term. 



Figure 22 represents the uppermost decile, that is to say the size above which lie 

 10 % of the tish. Here the difference between the inshore and the somewhat deeper water 

 stations is more pronounced; at the six former stations the upper decile stands at from 

 56 to 66 centimetres, while at the outer four stations it ranges from 75 centimetres to 84 

 centimetres. 



Fig. 22. Upper decile: or size (in centimetres) below which lie 90 p. c. of the Cod. 



Fig. 23. Mean number 

 of Cod caught per hour by Otter-trawl. 



Fig. 24. Percentage number 

 of Cod in the Total Catch of all fish. 



It is obvious that the extremes, that is to say the sizes of the very smallest and 

 very largest fish, are of little importance, for these extremes are represented generally by 

 single individuals, whose appearance is more or less fortuitous. The other points shown 

 in our Table may be studied with advantage, and the reader may easily chart them for 

 himself 



In figure 23 we show the average catch of Cod per hour in the Firth of Forth. In 

 this case the figures are not very regular, but they show on the whole, as might be ex- 

 pected, that the catch is largest on the grounds where the fish are on the average smallest 

 and youngest. Thus at the two outermost stations VIII and IX, and in a less degree at 

 VII also, the average catch per hour is' distinctly small, ranging from 15 to 28 cod. 



